Various guidance systems have been designed in the past for assisting an airborne vehicle in determining if it is following its intended flight path and if not to provide a correctional signal to the navigation apparatus. For example, U.S. Pat. No. 3,328,795 to Hallmark discloses a guidance system for ascertaining the flight path of an airborne vehicle over hilly terrain. The guidance system is provided with an altimeter arrangement for determining the difference in elevation from one radar pulsed area of the hilly terrain to another along the ground track of the vehicle. The computer of the system compares the reflected signals of the different pulsed areas of the hilly terrain with its data base in order to ascertain the vehicle flight path. U.S. Pat. No. 4,144,571 to Webber relates to another airborne vehicle guidance system for use only on hilly terrain. The system is generally made up of a processor for receiving data from storage, and also for receiving data of a radar sample of hilly terrain for indicating aircraft elevation. The processor includes a Kalman filter for resolving the aforesaid data into an updated three coordinate airborne position of the aircraft prior to the guidance system taking another radar sample of a hilly terrain section for another updated position of the aircraft along its flight path. U.S. Pat. No. 4,495,580 to Kearns discloses an airborne automated navigation system for automatically monitoring the position and velocity of an aircraft along its flight path while at the same time correcting the position of the aircraft when it is not along its intended path. The system is generally made of a radar altimeter, a navigation device, and a stored reference map. When sampled outputs of the navigation device and altimeter are correlated with the stored map, and such correlation, e.g., indicates that the aircraft is deviating from its intended path, a data register output of the system transmits a correction signal output to the navigation device so as to direct the aircraft flight control to follow the correct course. However, none of the aforediscussed references whether taken alone or in any combination remotely suggest the improved aircraft guidance system of the invention for controlling the operation of a navigation apparatus in maintaining the aircraft along its intended flight path (especially at a terminal fix) and even though the aircraft is flying over substantially flat terrain with random and different features therealong. The system is generally made up of a radar altimeter, a video signal processor and a master processor connected to both the altimeter and the signal processor. The altimeter transmits a series of pulses at predetermined time intervals for impacting a plurality of relatively spaced points along the ground track of the aircraft vehicle. The signal processor receives the echo signature of each radar-pulse impacted ground track point and is provided with means for dividing each signature into first and second signals. One of the divided signals is transformed and delayed and then recombined with the other divided signal so as to determine an intersection point between the signals. This point is a quantitized value of a given signature that indicates the average weighted reflectivity value of an annulus about a pulse-impacted ground-track point. The quantitized value of each signature is then transformed by the signal processor into digital form. The master processor receives the digital signal of each signature and combines same into a series of digital signals that represents a sample data array. The sample array is then compared with a series of digital arrays of a stored matrix for the purpose of substantially matching the sample array with one of the stored arrays thereby enabling an accurate determination of the vehicle flight path.